1. Field of the Invention
The invention relates in general to rotary actuators for tape and disk drives and, in particular, to a combined actuator mount and pivot member having no moving contact points that provides precise rotational movement of an actuator arm about an axis within an axial region and within a limited angular arc range.
2. Description of the Prior Art
Contemporary hard disk drives employ a rotary actuator arm within a hard disk support structure. Transducers or read/write heads are located at the end of the rotary actuator arm. During use, the arm is rotated to precisely position the read/write heads relative to data tracks located on the surface of storage/retrieval disks. Repeatability, that is, the ability of the heads to return to exactly the same location relative to the disks on every cycle, is absolutely essential. The storage/retrieval disks are rotatably mounted within the same hard disk support structure. The hard disk support structure includes a base, a cover, and a seal to protect the contents from environmental contamination. Often the actuator arm has a plurality of extended fingers supporting a plurality of transducer heads that track a plurality of storage/retrieval disks co-axially mounted in a single hard disk assembly.
The movement of the transducers must be controlled with great precision in order for the hard disk assembly to function properly. Thus, the rotational movement of the actuator arm must be controlled with great precision. The rotation must be free of looseness or backlash. The precise angular movement of the actuator arm is electro-magnetically controlled by regulating current travelling through a coil mounted on the actuator arm which is positioned between two permanent magnets. For a specific current value moving through the coil, the actuator arm is precisely rotated to a specific position. However, if there is too much rotational friction in the pivot structure, the actuator arm, in response to a specific current value, can be incorrectly positioned. Thus, conventional expedients had attempted to effect the rotation of the actuator arm with as little rotational friction resistance as possible since it had been believed that such undesirable friction can cause read/write errors.
Previous expedients generally provided precision roller bearings in the assembly to precisely control the rotational movement and positioning of the actuator arm. Precision roller bearings incorporate a plurality of ball bearings positioned between annular races. The ball bearings are often lubricated to further reduce friction. The lubricants within the sealed hard disk support structure had presented serious problems because of the potential that any lubricants that escaped from the bearings can undesirably contaminate the surfaces of the storage/retrieval disks in the assembly. An example of a roller bearing assembly utilized in a hard disk drive assembly is disclosed, for example, in U.S. Pat. No. 5,510,940 to Tacklind et al.
There are numerous drawbacks to the previous expedient of using precision roller bearings. One drawback is that they are relatively expensive components because each part in the bearing must be manufactured to exacting tolerances, which, in turn, increases their costs. Another drawback is that they must be assembled in a clean room to prevent the possibility of contamination. This also increases assembly costs. Still another drawback is that the rotational frictional resistance of a precision roller bearing changes responsive to temperature changes, minute irregularities in its components, changes in the characteristics of the lubricant, contaminants, and the like. These changes have resulted in read/write errors on the storage/retrieval disks, because the transducers do not return to exactly the same locations on the disks on every cycle. Attempts to solve this problem have undesirably increased the cost and complexity of the assembly. For example, in U.S. Pat. No. 5,628,571 to Ohta et al an additional preload spring is included to act against bearing races made from dissimilar metals in order to counter the effects of temperature variation. Other friction problems result from contaminants which, when present, must be overcome by the electromagnetic forces of the actuator. Such contaminants, when present, create a resistance that is inconsistent and non-repeatable. For example, an actuator arm could rotate 2 to 4 degrees with little or no frictional resistance until a contaminant particle, which happens to reside on a ball bearing, impacts a contact point in one of the races in the bearing. This contact creates an instantaneous increase in frictional resistance. This instantaneous increase in frictional resistance is not repeatable, predictable or consistent since contaminant particles can move or be crushed into multiple particles when inside a roller bearing. The problem can further be complicated when the particles cause wear or pitting of the ball bearing surfaces or races. Thus, generally the problem is not rotational friction per se, but rather intermittent, unpredictable and non-repeatable rotational resistance. When roller bearings are used, this problem is generally unsolvable because thermal variation, particulate contaminants, as manufactured irregularities, lubricant changes, wear and pitting, and the like are unavoidable.
There are other drawbacks as well in utilizing precision roller ball bearings. They are susceptible to damage when improperly handled. For instance, when subjected to drive and shock vibration tests, damage to the bearings had been observed. Such damage can cause the loss of designed preload, which causes backlash in the actuator arm assembly. Such backlash can result in catastrophic read/write errors. In addition, as technological advances in storage/retrieval disks continue, the number of data storage tracks per inch on the disks continues to increase. This requires even closer tolerances for the roller ball bearings. Achieving these greater roller bearing tolerances, even if physically possible, would undesirably further increase the cost of the assemblies. Thus, as more data tracks are placed on read/write disks, the problems that are inherent in the use of precision roller bearings in hard disk actuator arm assemblies are becoming very serious.
Due to the continued growth and competition in the computer industry, the need has arisen for mass-produced, inexpensive hard disk drive assemblies having improved performance and reliability characteristics. Thus, there is a need to reduce the cost of the hard disk drive assemblies by eliminating the use of precision roller bearings in the actuator arm pivot.
There have been some prior expedients proposed for the elimination of precision roller bearings in actuator arm pivot assemblies. In U.S. Pat. No. 5,355,268 to Schulze, a pin/cup pivot is disclosed establishing either rolling or sliding contact between the pin and cup. The pin is fixedly attached to the actuator arm and the cup is fixedly attached to the support structure. The pin/cup pivot configuration is not mount stable by itself, that is, it requires additional components to maintain the pin against the cup. For example, a magnetic system is disclosed to maintain the pin against the cup and thereby provide the required mount stability. Another attempt to eliminate the use of precision roller bearings is disclosed in U.S. Pat. No. 5,757,588 to Larson. A plurality of resilient fingers snappedly and slideably engage a pivot shaft fixed to the support structure. However, the mount stability of the pivot structure to shock loads is inherently limited by the elasticity of the resilient fingers on the pivot shaft.
All the prior art expedients rely on rolling and/or sliding contact points in the pivot area. Undesirably, some form of lubrication and/or protection from contaminants is required. Temperature variations also pose problems for these rolling or sliding contact based expedients. Temperature variations can alter the rotational frictional resistance of the pivot structure and thereby undesirably result in read/write errors for the hard disk assembly.
Therefore, there is a need to provide a less complicated, less expensive, more reliable pivot structure for mounting hard disk actuator arms. There is also a need to provide a pivot structure that has no moving or rolling contact points. There is also a need to provide a bearingless pivot structure that provides its own mount stability in order to counter shock loads, without additional components or systems. There is also a need to provide a pivot structure that requires no lubrication or contamination protection, and does not wear or pit.
These and other difficulties of the prior art have been overcome according to the present invention.
A preferred embodiment of the combined actuator mount and pivot assembly according to the present invention comprises a flexible cantilever member fixedly engaged to a base mount structure at one end and fixedly engaged to an actuator cartridge member at the other end. Flexing the flexible cantilever member along a hinge line between the base mount structure and the actuator cartridge member causes rotational movement of the rotary actuator arm through an arc of from approximately 20 to 50 degrees, more or less. The flexible cantilever member also supports the rotary actuator arm in operative position with respect to the disks. The rotary actuator arm is thus mounted to the frame of a hard drive through a flexible hinge that has no moving parts. The flexible hinge permits the rotary actuator arm to pivot through an arc of limited extent with a very high degree of positional repeatability. The physical dimensions and properties of the member or members that form the flexible hinge are selected so that it does not stretch in any direction in the hinge area and will flex without suffering bending fatigue for the expected life of the hard drive. Importantly, when the pivot cartridge rotates, there are no moving contact points, slack, or backlash. While not wishing to be bound by any theory of operation, it is believed the hinge line is a small axial region within which the rotary actuator arm rotates about an instantaneous axis at any given position within a limited angular arc range. For a given angular position the position of the instantaneous axis is substantially identical in every cycle. The positioning of the read/write heads is thus repeatable from cycle to cycle.
According to one embodiment, the actuator cartridge member has an outer cylindrical surface that can be inserted into a mount hole in an actuator arm and fixed therein, making the bearingless pivot cartridge assembly interchangeable with prior art precision roller bearing cartridges.
The cantilever member should be substantially non-elastic in a direction extending between its opposed ends and be highly resistant to fatigue failure due to bending. Any elongation of the cantilever member in the plane of the cantilever member or twisting of the cantilever member out of that plane would substantially impair the repeatability of the system. Non-elastic organic polymers have been found to serve well as the material for the cantilever member. It has been found, for example, that polyimide films posses the required non-elastic characteristic in a direction extending between the ends of the film while not suffering from fatigue failure. In a preferred embodiment, an about 0.005 inch thick polyimide film material is used to form the cantilevered member. It is non-elastic, exhibits no bending fatigue over the expected life of the hard drive, and its bending resilience is such that the electromagnetic controls of the actuator arm generally need not be modified to accommodate it in most hard drive configurations. Although in a preferred embodiment the cartridge assembly is adapted to replace conventional roller bearing cartridge assemblies, the cantilever member and base mount structure subassembly could be directly installed to the actuator arm, if desired. The cantilever member can conveniently take the form of a panel having a length at least at the hinge line that is at least 50, and preferably 100 times the thickness of the panel. The panel can be a single piece or several pieces, provided the inelastic and non-warping characteristics at the hinge line are maintained.